Normal FunctionThe MAOA gene provides instructions for making an enzyme called monoamine oxidase A. This enzyme is part of a family of enzymes that break down molecules called monoamines through a chemical reaction known as oxidation. Among the monoamines broken down by monoamine oxidase A are certain chemicals that act as neurotransmitters, which transmit signals between nerve cells in the brain. Neurotransmitters are broken down when signaling is no longer needed.

Specifically, monoamine oxidase A is involved in the breakdown of the neurotransmitters serotonin, epinephrine, norepinephrine, and dopamine. Signals transmitted by serotonin regulate mood, emotion, sleep, and appetite. Epinephrine and norepinephrine control the body's response to stress. Dopamine transmits signals within the brain to produce smooth physical movements.

Monoamine oxidase A also helps break down monoamines found in the diet. It seems to be particularly important in the breakdown of excess tyramine, which is found in cheese and other foods.

Monoamine oxidase A appears to be involved in normal brain development before birth. The enzyme plays a role in the controlled self-destruction of cells (apoptosis), which is an important process in the development of many tissues and organs, including the brain.

Monoamine oxidase A deficiencyMutations in the MAOA gene cause monoamine oxidase A deficiency. This condition affects males almost exclusively and is characterized by mild intellectual disability and behavioral problems, including aggressive and violent outbursts. In some cases, particular foods seem to worsen symptoms of the condition. The MAOA gene mutations reduce monoamine oxidase A activity, which causes serotonin and other neurotransmitters to build up in the brain. It is unclear how this buildup leads to the signs and symptoms of monoamine oxidase A deficiency. Researchers speculate that an excess of certain neurotransmitters, particularly serotonin and norepinephrine, may impair an affected individual's ability to control his impulses, leading to aggressive outbursts. Some studies suggest that reduced monoamine oxidase A activity alters development of certain regions of the brain, which may contribute to intellectual disability and behavioral problems in people with monoamine oxidase A deficiency. Researchers suspect that a buildup of tyramine can contribute to the problems associated with the condition, which may be why foods high in this molecule can worsen symptoms.